Arsenic-containing waste residue added paving stone and preparation method thereof

Abstract

The invention relates to the technical field of paving stones, in particular to an arsenic-containing waste residue-added paving stone and a preparation method thereof, the arsenic-containing waste residue-added paving stone comprises the following raw materials: carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate and water; each core-shell waste residue particle sequentially comprises a waste residue inner core layer and a barrier wrapping layer from inside to outside; the waste residue inner core layer comprises the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residues, phosphate and water; the barrier wrapping layer comprises the following raw materials in parts by mass: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water. According to the paving stone added with the arsenic-containing waste residues, the arsenic-containing waste residues are applied to the paving stone, on the premise that the production cost is reduced, the paving stone not only has excellent and lasting extremely-low arsenic leaching toxicity, but also can improve the mechanical property and durability of the paving stone so as to overcome the defects in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of paving stones, and in particular to a paving stone added with arsenic-containing waste residue and a preparation method thereof. Background Art

[0002] Arsenic has attracted much attention from all walks of life due to its high toxicity and volatility. However, in the current basic smelting and chemical production process, arsenic flows with the material and is ultimately stored in various slag phases and tailings in a combined state, hindering resource utilization and safe disposal. Therefore, the stabilization and disposal of arsenic-containing waste slag is a major problem that needs to be solved in the current smelting and chemical industries.

[0003] In order to solve the above problems, traditional technologies mainly use the following technical means to treat arsenic-containing waste slag as a resource: (1) Pyrometallurgical treatment, in which arsenic-containing waste slag is subjected to oxidation roasting, reduction roasting or vacuum roasting to obtain arsenic-containing vapor separated from other materials. The arsenic-containing vapor is then subjected to secondary oxidation and dust collection to obtain As 2 O 3 , but pyrometallurgical treatment has the disadvantages of serious environmental pollution, large investment and small raw material adaptability; (2) Wet arsenic extraction, through acid leaching, alkali leaching or salt leaching, arsenic is separated from arsenic-containing waste slag in the form of arsenate, and further refined to obtain arsenic trioxide. The wet arsenic extraction process has low energy consumption, less pollution and high efficiency, but the process is complicated and the processing cost is very high. However, although the above resource recovery methods have alleviated the pollution and harm of arsenic-containing waste slag to the environment to a certain extent and realized the resource utilization of arsenic-containing waste slag, they also have problems such as low recovery efficiency and relatively limited arsenic product market.

[0004] In order to overcome the above-mentioned defects, the prior art uses a composite curing agent obtained by mixing lime, polyferric sulfate, dolomite and cement, and uses the composite curing agent to cure the arsenate in the arsenic-containing waste residue to obtain a solidified body (i.e., paving stones). However, due to the volume shrinkage of calcium silicate hydrate, one of the hydration products of cement, microcracks and pores are formed in the paving stones, resulting in poor mechanical properties of the paving stones using cement as the gel material. In addition, tricalcium aluminate, another hydration product of cement, easily reacts with water in the system to form calcium sulfonate in the presence of sulfate ions (provided by polyferric sulfate). Arsenate easily partially replaces sulfate ions in calcium sulfonate to form arsenic-type calcium sulfonate (Ca sulfonate). 6 Al 2 (SO 4 ) 3-x (AsO 4 ) x (OH)12.26H 2O), the volume of this arsenical ettringite will significantly expand during the crystallization growth process, resulting in local stress concentration inside the paving stone. It should be noted that due to the spatio-temporal difference between the volume shrinkage of calcium silicate hydrate and the expansion of arsenical ettringite, the volume shrinkage of calcium silicate hydrate and the expansion of arsenical ettringite cannot offset each other. And because cement itself is prone to forming pores, the tensile strength of the material is relatively low, making it easy for stress to exceed the tensile strength, thus easily inducing the initiation and propagation of microcracks, and finally forming through-cracks, further reducing the mechanical properties of the paving stone. At the same time, through-cracks are prone to increasing the porosity, making it easy for water and harmful substances to invade, thereby reducing the durability of the paving stone. In addition, in an acidic environment, the protonation tendency of arsenate is high and the lattice distortion is large, making arsenical ettringite prone to decomposition in an acidic environment, which not only causes the paving stone to be prone to cracking in an acidic environment, affecting the durability of the paving stone, but also easily leads to the secondary release of arsenate, resulting in an increase in the leaching toxicity of arsenic. Even if the arsenic leaching concentration of the paving stone not immersed in an acidic environment ≤ 0.3 mg / L meets the limit requirement of 1.2 mg / L in the "Identification Standard for Leaching Toxicity of Hazardous Wastes - GB18598-2019", but under long-term immersion in an acidic environment, its arsenic leaching concentration is prone to exceeding the standard and it is difficult to meet the strict requirement of arsenic leaching concentration ≤ 0.3 mg / L under long-term acidic environment. In addition, due to the use of cement as a raw material, the cost of the paving stone is relatively high.

[0005] Therefore, the existing paving stones have defects such as poor mechanical properties, insufficient durability, high arsenic leaching toxicity and high cost. Summary of the Invention

[0006] The purpose of the present invention is to propose a paving stone added with arsenic-containing waste residue. By applying the arsenic-containing waste residue to the paving stone, on the premise of reducing the production cost, it not only has excellent and lasting extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone to overcome the deficiencies in the prior art.

[0007] Another purpose of the present invention is to propose a preparation method of a paving stone added with arsenic-containing waste residue. The preparation method is simple and has strong operability. It not only has excellent and lasting extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone.

[0008] To achieve this purpose, the present invention adopts the following technical solutions: A paving stone added with arsenic-containing waste residue, comprising the following raw materials: carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate and water; wherein, the particle size of the core-shell waste residue particles is 7 - 13 mm; calculated by mass percentage, the content of calcium hydroxide in the carbide slag ≥ 8%; The core-shell waste residue particles sequentially include a waste residue inner core layer and a barrier wrapping layer from the inside to the outside; The waste residue core layer comprises the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water; wherein, the mineral composition of the arsenic-containing waste residue includes arsenopyrite; the mineral composition of the red mud includes goethite, and the chemical composition of the red mud includes CaO; Calculated by mass parts, the barrier coating layer comprises the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water; The chemical composition of the slag powder in both the waste residue core layer and the barrier coating layer includes SiO 2 、Al 2 O 3 and CaO.

[0009] Further, calculated by mass parts, the paving stone comprises the following raw materials: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste residue particles, 26-30 parts of fine aggregate and 7-8 parts of water; Calculated by mass parts, the waste residue core layer comprises the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste residue, 0.1-0.5 parts of phosphate and 7-10 parts of water.

[0010] Further, the particle size of the arsenic-containing waste residue is <75 μm, and the specific surface area is >350 m 2 / g.

[0011] Further, calculated by mass percentage, the chemical composition of the slag powder in both the waste residue core layer and the barrier coating layer includes SiO 2 40-55%, Al 2 O 3 24-28%, Fe 2 O 3 5-7% and CaO 5-8%, and the rest is loss on ignition.

[0012] Further, calculated by mass percentage, the chemical composition of the red mud includes Al 2 O 3 15-20%, SiO 2 5-15%, Fe 2 O 3 30-40%, CaO 5-10% and Na 2 O 5-10%, and the rest is loss on ignition.

[0013] Further, the modulus of the sodium silicate is 1.2-1.4.

[0014] Further, calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH) 2 85 - 90%, SiO 2 3 - 3.5%, Fe 2 O 3 0.8 - 1%, Al 2 O 3 2 - 2.5% and MgO 0.8 - 1%, and the rest is loss on ignition.

[0015] Further, the flexural strength of the paving stone is ≥5 MPa, the compressive strength is ≥48 MPa, the arsenic leaching concentration before soaking in the acetic acid buffer solution with a pH of 2.88 is ≤0.2 mg / L, and the arsenic leaching concentration after soaking in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3 mg / L.

[0016] Further, the steps for preparing the paving stone added with arsenic - containing waste residue include the following: A. Prepare core - shell waste residue particles; Mix the formulated amounts of magnesium oxide, mineral powder, slag powder, red mud, arsenic - containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and after drying, obtain a waste residue inner core layer; Mix the formulated amounts of slag powder, mineral powder, sodium silicate and water evenly to obtain a barrier coating slurry; Soak the waste residue inner core layer in the barrier coating slurry, take it out, and after steam curing and room - temperature curing, form a barrier coating layer on the surface of the waste residue inner core layer to obtain core - shell waste residue particles; B. Prepare paving stone: Mix the formulated amounts of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material; Mix the core - shell waste residue particles, fine aggregate and the gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, vibrate and press to obtain a plate; after sealing the plate and performing steam curing and room - temperature curing, obtain the paving stone.

[0017] Further, in steps A and B, the curing temperature of the steam curing is 60 - 70 °C, and the curing time is 48 - 74 h; the curing time of the room - temperature curing is 168 - 240 h.

[0018] The technical solution provided by the present invention may include the following beneficial effects: 1. The mineral composition of the arsenic - containing waste residue includes arsenopyrite. In the natural environment, arsenopyrite is easily oxidized and gradually generates free and highly toxic AsO 4 3- . In an aqueous environment, MgO hydrolyzes to generate Mg 2+ , Mg 2+It can react with AsO 4 3- to form magnesium arsenate precipitate, realizing the fixation of arsenic. At the same time, the mineral composition of red mud includes goethite, and the surface of goethite is rich in hydroxyl groups that can form stable complexes with AsO 4 3- through coordination bonds, further realizing the fixation of arsenic. In addition, the hydrolysis of magnesium oxide can produce OH - to make the formulation system alkaline, and phosphate can also produce OH - through the hydrolysis of phosphate ions, increasing the alkalinity of the formulation system. The chemical composition of slag powder includes CaO, and the chemical composition of ore powder (generally referring to the powder obtained by crushing and processing the mined ore) itself also includes CaO, and the chemical composition of red mud also includes CaO. In an aqueous and alkaline environment, the structures of slag powder, ore powder and red mud are damaged, so that the activity of CaO is activated to release Ca 2+ Ca 2 + can react with AsO 4 3- to form calcium arsenate precipitate, also realizing the fixation of arsenic.

[0019] 2. The chemical composition of slag powder also includes SiO 2 and Al 2 O 3 , and the chemical composition of ore powder itself also includes SiO 2 and Al 2 O 3 . Al 2 O 3 in slag powder and ore powder all exist in the form of an aluminum-oxygen network structure. In a strong alkaline environment, the aluminum-oxygen network structure dissociates and instantaneously generates Al 3+ , which is then surrounded by OH - and generates [Al(OH) 4 - (i.e., aluminate). At the same time, in an alkaline environment, Mg 2+ produced by the hydrolysis of magnesium oxide, OH - and the transiently generated Al 3+ react to form a positively charged lamellar through coprecipitation, and the positively charged lamellar adsorbs AsO 4 3- through electrostatic interaction and / or intercalation, generating arsenate intercalated aluminum-magnesium hydrotalcite (Mg 6 Al 2 (OH) 16 (AsO 4 ) 0.5 ·4H 2 O), thus realizing the fixation of arsenic. ​

[0020] 3. SiO in slag powder and mineral powder 2 exists in the form of a silicon-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure depolymerize to form silicate anions (including low-polymerization-degree silicate anions SiO 4 4- and high-polymerization-degree silicate anions [SiO 3 n 2- ). The silicate anions, Mg 2+ produced by the hydrolysis of magnesium oxide, and OH - react to form magnesium silicate hydrate (Mg 3 Si 2 O 5 (OH) 4 ). And AsO 4 3- can form a coordination structure with Mg 2+ on the surface of magnesium silicate hydrate through electrostatic interaction, realizing the adsorption and fixation of arsenic on the surface of magnesium silicate hydrate; at the same time, AsO 4 3- can partially replace the magnesium-oxygen tetrahedron unit in magnesium silicate hydrate to form a Mg x-1 AsO 4 (Si y O 2y+1 )·nH 2 O intercalation structure, which can not only realize the adsorption and fixation of arsenic inside magnesium silicate hydrate, but also release Mg 2+ in the magnesium-oxygen tetrahedron into the formulation system, and the released Mg 2+ can react with AsO 4 3- in the system to form magnesium arsenate precipitate, thus further realizing the fixation of arsenic. In addition, the oxygen atoms in AsO 4 3- can combine with magnesium silicate hydrate through hydrogen bonds or covalent bonds to form a composite structure, which can also fix arsenic.

[0021] 4. The denser barrier coating layer can not only encapsulate AsO 4 3- in the inner core layer of the waste residue through chemical action to realize the fixation of arsenic, but also prevent the leaching of AsO 4 3- in the inner core layer of the waste residue by virtue of its physical barrier effect, which is beneficial to reducing the leaching toxicity of arsenic. At the same time, this barrier coating layer has high acid and alkali resistance. Even in an acidic or alkaline environment, AsO 4 3-It is also not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. The above-mentioned multi-faceted effects make the arsenic leaching concentration of the paving stone before being immersed in the acetic acid buffer solution with a pH of 2.88 ≤ 0.2 mg / L, and the arsenic leaching concentration after being immersed in the acetic acid buffer solution with a pH of 2.88 for 30 days ≤ 0.3 mg / L, having excellent and persistent extremely low arsenic leaching toxicity. In addition, the barrier coating layer has a relatively high strength, forming a hard shell layer outside the waste residue core layer, making the core-shell waste residue particles have a relatively high strength, thereby enhancing the mechanical properties of the paving stone. Detailed implementation manners

[0022] The present technical solution provides a paving stone added with arsenic-containing waste residue, which comprises the following raw materials: carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate and water; wherein, the particle size of the core-shell waste residue particles is 7-13 mm; calculated by mass percentage, the content of calcium hydroxide in the carbide slag ≥ 8%; The core-shell waste residue particles sequentially comprise a waste residue core layer and a barrier coating layer from the inside to the outside; The waste residue core layer comprises the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water; wherein, the mineral composition of the arsenic-containing waste residue comprises arsenopyrite; the mineral composition of the red mud comprises goethite, and the chemical composition of the red mud comprises CaO; Calculated by mass parts, the barrier coating layer comprises the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water; The chemical compositions of the slag powder in the waste residue core layer and the barrier coating layer both comprise SiO 2 、Al 2 O 3 and CaO.

[0023] Aiming at the defects of poor mechanical properties, insufficient durability, high arsenic leaching toxicity and high cost existing in the paving stones in the prior art, the present technical solution proposes a paving stone added with arsenic-containing waste residue. By optimizing the ratio design and raw materials of the paving stone, the waste residue core layer and the barrier coating layer, the arsenic-containing waste residue is applied to the paving stone. On the premise of reducing the production cost, it not only has excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone to meet the actual use requirements.

[0024] Specifically, the raw materials of the waste residue core layer include magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water; wherein, the mineral composition of the arsenic-containing waste residue includes arsenopyrite. In the natural environment, arsenopyrite is easily oxidized and gradually generates free and highly toxic AsO 4 3- . In an aqueous environment, MgO hydrolyzes to generate Mg 2+ , Mg2+ It can react with AsO 4 3- to form magnesium arsenate precipitate, realizing the fixation of arsenic. At the same time, the mineral composition of red mud includes goethite, and the surface of goethite is rich in hydroxyl groups that can form stable complexes with AsO 4 3- through coordination bonds, further realizing the fixation of arsenic. In addition, the hydrolysis of magnesium oxide can produce OH - to make the formulation system alkaline, and phosphate can also produce OH - through the hydrolysis of phosphate groups, increasing the alkalinity of the formulation system. The chemical composition of slag powder includes CaO, and the chemical composition of ore powder (generally refers to the powder obtained by crushing and processing the mined ore) itself also includes CaO, and the chemical composition of red mud also includes CaO. In an aqueous and alkaline environment, the structures of slag powder, ore powder and red mud are damaged, so that the activity of CaO is activated to release Ca 2+ Ca 2+ can react with AsO 4 3- to form calcium arsenate precipitate, which can also realize the fixation of arsenic.

[0025] Furthermore, in an aqueous and alkaline environment, the activation of the activity of CaO in slag powder, ore powder and red mud can also produce OH - , which cooperate with the OH - produced by the hydrolysis of magnesium oxide and phosphate hydrolysis to make the waste residue inner layer formulation system present a strong alkaline environment.

[0026] At the same time, the chemical composition of slag powder also includes SiO 2 and Al 2 O 3 , and the chemical composition of ore powder itself also includes SiO 2 and Al 2 O 3 . Al 2 O 3 in slag powder and ore powder all exist in the form of an aluminum-oxygen network structure. In a strong alkaline environment, the aluminum-oxygen network structure dissociates and instantaneously generates Al 3+ , which is then surrounded by OH - and generates [Al(OH) 4 - (i.e., aluminate). At the same time, in an alkaline environment, Mg 2+ , OH - produced by the hydrolysis of magnesium oxide and the transiently generated Al 3+ react to form a positively charged lamellar through coprecipitation, and the positively charged lamellar adsorbs AsO 4 3- ​, generate arsenate intercalated magnesium aluminum hydrotalcite (Mg 6 Al 2 (OH) 16 (AsO 4 ) 0.5 ·4H 2 O), thereby achieving the fixation of arsenic.

[0027] In addition, SiO in slag powder and mineral powder 2 both exist in the form of a silicon-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure depolymerize to generate silicate anions (including low-polymerization-degree silicate anions SiO 4 4- and high-polymerization-degree silicate anions [SiO 3 n 2- ). The silicate anions, Mg 2+ produced by the hydrolysis of magnesium oxide, and OH - react to form magnesium silicate hydrate (Mg 3 Si 2 O 5 (OH) 4 ). And AsO 4 3- can form a coordination structure with Mg 2+ on the surface of magnesium silicate hydrate through electrostatic interaction, achieving the adsorption and fixation of arsenic on the surface of magnesium silicate hydrate; at the same time, AsO 4 3- can partially replace the magnesium-oxygen tetrahedron unit in magnesium silicate hydrate to form a Mg x-1 AsO 4 (Si y O 2y+1 )·nH 2 O intercalation structure, which can not only achieve the adsorption and fixation of arsenic inside magnesium silicate hydrate, but also release Mg 2+ in the magnesium-oxygen tetrahedron into the formulation system, and the released Mg 2+ can react with AsO 4 3- in the system to form magnesium arsenate precipitate, thereby further achieving the fixation of arsenic. In addition, the oxygen atoms in AsO 4 3- can combine with magnesium silicate hydrate through hydrogen bonds or covalent bonds to form a composite structure, which can also fix arsenic.

[0028] In addition, low-polymerization-degree silicate anions tend to react with Ca 2+ produced by CaO in slag powder and mineral powder in an alkaline environment to form calcium silicate gel, and in this system, aluminate anions will replace part of the silicate anions and enter the interior of the calcium silicate gel to form calcium aluminosilicate gel; high-polymerization-degree silicate anions tend to react with Mg 2+The reaction generates magnesium silicate gel, and Ca generated by CaO in slag powder and ore powder under an alkaline environment 2+ enters the interior of the magnesium silicate gel to generate calcium magnesium silicate gel. That is, the present formulation system finally forms a hybrid gel network structure of magnesium silicate gel and calcium aluminosilicate gel, and the hybrid gel network structure can form calcium magnesium silicate gel that wraps the arsenic-containing waste residue, thereby realizing the fixation of arsenic.

[0029] In summary, the fixation of arsenic is achieved through the mutual cooperation of the above-mentioned various effects in the waste residue inner core layer of the present technical solution.

[0030] Furthermore, the hybrid gel network structure has the high strength of calcium aluminosilicate gel, which is beneficial to improving the strength of the waste residue inner core layer, thereby improving the strength of the paving stone; at the same time, the hybrid gel network structure can increase the compactness of the waste residue inner core layer, which is also beneficial to further improving the strength of the paving stone. In addition, the hybrid gel network structure has the acid resistance of magnesium silicate gel, which is beneficial to improving the durability of the waste residue inner core layer, thereby improving the durability of the paving stone.

[0031] Therefore, the waste residue inner core layer is obtained by compounding magnesium oxide, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water in the present technical solution. Not only turning waste into treasure and making full use of the arsenic-containing waste residue, but also while fixing AsO in the arsenic-containing waste residue 4 3- and reducing the arsenic leaching toxicity, it is also beneficial to improve the mechanical properties and durability of the paving stone.

[0032] It should be noted that the synergistic effect among the three raw materials of ore powder, slag powder and red mud in the waste residue inner core layer can provide sufficient calcium for the system, and the following effects will be produced: (1) Silicate radicals can react with Mg generated by the hydrolysis of MgO 2+ to generate magnesium silicate gel, and the main structure of the magnesium silicate gel is composed of magnesium octahedrons and silicon oxygen tetrahedrons, forming a layered structure similar to talc. However, the interlayer bonding of pure magnesium silicate gel is weak, which easily leads to a loose structure, reducing the compressive strength and durability. And the Ca 2+ provided by ore powder, slag powder and red mud has a larger ionic radius than Mg 2+ , and it can partially replace the Mg 2+ sites or be embedded in the interlayer of the magnesium silicate gel, balancing the negative charge of the silicon oxygen chain through electrostatic interaction, enhancing the interlayer connection of the magnesium silicate gel, and improving the structural density; (2) The Ca 2+ provided by ore powder, slag powder and red mud can reduce the nucleation energy barrier of the magnesium silicate gel, and together with Mg 2+ promote the formation of the early gel phase, optimizing the generation of the hybrid gel network structure in the waste residue inner core layer; (3) Ca 2+ tends to combine with silicate radicals with low polymerization degree, while Mg2+ It is more likely to react with silicate radicals with high polymerization degree. The synergistic effect of the two can form a more uniform gel structure, improving mechanical properties and durability. (4) When there is no Ca in the system 2+ present, Mg 2+ is prone to react with OH - to generate brittle magnesium hydroxide (Brucite), destroying the continuity of the calcium magnesium silicate gel. While Ca 2+ inhibits the formation of Brucite through competitive reaction, maintaining the dominance of layered calcium magnesium silicate gel, which is beneficial to maintaining the overall properties of the material. In summary, the introduction of mineral powder, slag powder and red mud in the waste residue inner core layer significantly improves the strength and durability of the waste residue inner core layer through four mechanisms: structural strengthening, nucleation promotion, silicate radical binding optimization and brittle phase inhibition.

[0033] Secondly, although the waste residue inner core layer can fix AsO 4 3- in the arsenic-containing waste residue, thereby reducing the leaching toxicity of arsenic, due to its limited arsenic fixation ability, it is still difficult to meet the actual use requirements. Therefore, in this technical solution, a barrier coating layer is additionally provided outside the waste residue inner core layer. The barrier coating layer with higher density can not only wrap AsO 4 3- in the waste residue inner core layer through chemical action to achieve arsenic fixation, but also prevent the leaching of AsO 4 3- in the waste residue inner core layer by virtue of its physical barrier effect, which is beneficial to reducing the leaching toxicity of arsenic. At the same time, the barrier coating layer has high acid and alkali resistance. Even in an acidic or alkaline environment, AsO 4 3- in the arsenic-containing waste residue is not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. The above-mentioned multi-faceted effects make the arsenic leaching concentration of the paving stone ≤ 0.2 mg / L before being immersed in the acetic acid buffer solution with pH 2.88, and the arsenic leaching concentration ≤ 0.3 mg / L after being immersed in the acetic acid buffer solution with pH 2.88 for 30 days, having excellent and persistent extremely low arsenic leaching toxicity. In addition, the barrier coating layer has relatively high strength, forming a hard shell layer outside the waste residue inner core layer, making the core-shell waste residue particles have relatively high strength, thereby enhancing the mechanical properties of the paving stone.

[0034] Specifically, the raw materials of the barrier coating layer include slag powder, mineral powder, sodium silicate and water. When sodium silicate is added to the barrier coating layer formula, sodium silicate undergoes a hydrolysis reaction with water to generate OH - , making the formula system alkaline. At the same time, SiO 2 in both slag powder and mineral powder exists in the form of a silicon-oxygen network structure, and Al 2 O 3It exists in the form of an alumina-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure and the alumina-oxygen chains in the alumina-oxygen network structure are depolymerized, generating silicate ions and aluminate ions respectively. Since the addition amount of sodium silicate in the barrier coating formulation system is 7 to 8 parts, the Na + provided by sodium silicate is significantly in excess. Silicate ions and aluminate ions directly polycondense in the presence of excess Na + in the system to form sodium aluminosilicate gel (N-A-S-H) with a three-dimensional network structure. At the same time, silicate ions can react with the product Ca(OH) 2 formed after the activation of the activity of CaO in slag powder and mineral powder in the system, forming calcium silicate gel mainly with a layered structure, and in this system, aluminate ions replace part of the silicate ions and enter the interior of the calcium silicate gel to form calcium aluminosilicate gel (C-A-S-H). That is, the present formulation system finally forms a hybrid gel network structure composed of calcium aluminosilicate gel and sodium aluminosilicate gel. The hybrid gel network structure can not only wrap AsO 4 3- in the inner core layer of the waste residue to achieve the fixation of arsenic, but also endow the barrier coating with high density, enabling the barrier coating to block the leaching of arsenic-containing substances in the inner core layer of the waste residue through a physical barrier. At the same time, the hybrid gel network makes the barrier coating formulation system have both the acid and alkali resistance of sodium aluminosilicate gel, endowing the barrier coating with high acid and alkali resistance, so that even in acidic and alkaline environments, AsO 4 3- in the arsenic-containing waste residue is not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. In addition, the hybrid gel network can not only make the barrier coating formulation system have both the cementation strength of calcium aluminosilicate gel, but also endow the barrier coating with high density, which is also beneficial to improving the strength of the barrier coating, thereby being beneficial to improving the strength of the barrier coating.

[0035] Again, the raw materials of the paving stone in this technical solution include carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate and water. Carbide slag is a by-product of the reaction of calcium carbide with water to produce acetylene, and Ca(OH) 2 in carbide slag can form an alkaline environment. SiO 2 in mineral powder exists in the form of a silicon-oxygen network structure, and Al 2 O 3 in mineral powder exists in the form of an alumina-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure and the alumina-oxygen chains in the alumina-oxygen network structure are depolymerized, generating silicate ions and aluminate ions respectively. Silicate ions can react with the product Ca(OH) 2A reaction occurs to form calcium silicate gel mainly in a layered structure, and in this system, aluminate replaces silicate and enters the interior of the calcium silicate gel to form calcium aluminosilicate gel. The calcium aluminosilicate gel can adhere to the surfaces of the core-shell waste residue particles (acting as coarse aggregates) and fine aggregates, and wrap and bond the core-shell waste residue particles and fine aggregates, enabling the paving stones to bond into a whole and ensuring the strength of the paving stones.

[0036] Meanwhile, the calcium aluminosilicate gel formed in this application has a nano-particle accumulation structure, and its structure is denser than the gel formed by cement, which is beneficial to improving the strength of the paving stones. Further, the denser calcium aluminosilicate gel is beneficial to improving the tensile strength of the paving stones, and the stress generated during the crystallization process of ettringite is smaller than that of arsenical ettringite. Even if ettringite is formed in the paving stone formulation system, the relatively low stress generated during the crystallization process of ettringite is not likely to exceed the tensile strength and form through cracks, thus being beneficial to ensuring the strength of the paving stones.

[0037] In addition, desulfurized gypsum is a by-product of industrial flue gas desulfurization in coal-fired power plants, steel plants, etc. (mainly using the limestone-gypsum wet desulfurization process). In an alkaline environment, calcium sulfate dihydrate in the desulfurized gypsum dissolves and gradually releases sulfate ions and Ca 2+ , moreover, carbide slag can also provide Ca 2+ . In an aqueous and alkaline environment, sulfate ions, aluminate and Ca 2+ react to form ettringite, and the ettringite can fill the pores of the paving stones, improve the compactness, and thus increase the strength of the paving stones.

[0038] In addition, the core-shell waste residue particles with higher strength are mutually interlocked to form the framework of the paving stones, providing the function of supporting the paving stones, which is beneficial to endowing the paving stones with mechanical properties such as higher flexural strength and compressive strength; meanwhile, the fine aggregates can fill the voids in the paving stones, improve the compactness of the paving stones, reduce the risk of shrinkage and cracking, and thus enhance the mechanical properties such as compressive strength and flexural strength of the paving stones.

[0039] In summary, the above-mentioned multi-faceted effects in this application are beneficial to ensuring the mechanical properties such as compressive strength and flexural strength of the paving stones.

[0040] Further, in this technical solution, the inner core layer of the waste residue itself can fix arsenic by forming insoluble precipitates of AsO 4 3- and adsorbing and fixing AsO 4 3- ; while the barrier wrapping layer can block the leaching of AsO 4 3- in the inner core layer of the waste residue through physical and chemical actions, and further realize the fixation of AsO 4 3-Immobilization, the combined action of the above two aspects makes AsO in the core-shell waste residue particles 4 3- The leaching is extremely low. Therefore, the situation of AsO 4 3- replacing the sulfate radical in ettringite in this technical solution can be ignored, making the ettringite formed by this technical solution basically ordinary ettringite. Compared with arsenic-type ettringite, the volume expansion of ordinary ettringite is relatively low, which can stably fill the pores, avoiding the significant volume expansion generated during the crystallization growth of arsenic-type ettringite, and then causing local stress concentration inside the material, which is likely to trigger the generation of through cracks, thereby avoiding the intrusion of moisture and harmful substances into the interior of the paving stone, which is beneficial to improving the durability of the paving stone.

[0041] At the same time, due to the strong bonding effect between sulfate ions and Ca 2+ and Al 3+ in ordinary ettringite, ordinary ettringite is not easily decomposed in an acidic environment, which is also beneficial to avoiding the extremely rapid decomposition of arsenic-type ettringite in an acidic environment and avoiding the problem of the decrease in the durability of the paving stone.

[0042] In addition, as described before, since the calcium aluminosilicate gel formed in this technical solution has a nano-particle stacking structure and its structure is relatively dense, the paving stone of this technical solution is not easily formed with through cracks, which is also beneficial to ensuring the durability of the paving stone. In addition, the filling effect of the fine aggregate and the skeleton effect of the core-shell waste residue particles in this technical solution are also beneficial to ensuring the durability of the paving stone.

[0043] In summary, the above-mentioned multiple aspects of this application are beneficial to ensuring the durability of the paving stone.

[0044] Therefore, by treating the arsenic-containing waste residue, this technical solution not only turns waste into treasure and makes full use of the arsenic-containing waste residue, but also fixes the AsO 4 3- in the arsenic-containing waste residue, so that the paving stone has excellent and lasting extremely low arsenic leaching toxicity. At the same time, the core-shell waste residue particles prepared by this technical solution have extremely high strength. Adding them to the paving stone formula is not only beneficial to reducing costs, but also makes the paving stone have mechanical properties such as higher flexural strength and compressive strength. In addition, by optimizing the paving stone formula and there is basically no generation of arsenic-type ettringite in the paving stone formula, which is beneficial to improving the durability of the paving stone to meet the use requirements.

[0045] It should be noted that the raw material phosphate in the inner core layer of the waste residue in this scheme can be potassium phosphate, sodium phosphate, ammonium phosphate, etc., and the specific types are not limited here.

[0046] Preferably, calculated by mass percentage, the mineral components of the arsenic-containing waste residue include 5-30% arsenopyrite, 10-50% pyrite, 20-60% quartz, and 1-15% secondary arsenate.

[0047] Preferably, the particle size of the waste residue inner core layer is 5-10 mm, and the thickness of the barrier coating layer is 2-3 mm.

[0048] This technical solution limits the particle size of the waste residue inner core layer and the thickness of the coating layer, which is not only beneficial to ensuring the strength of the core-shell waste residue particles and the fixing effect on AsO 4 3- but also beneficial to ensuring its strength, thus being beneficial to ensuring the performance of the paving stone.

[0049] Preferably, the fine aggregate is any one of granite, limestone, and feldspar, and the particle size of the fine aggregate is 0.075-0.3 mm.

[0050] Granite, limestone, and feldspar are all hard rocks, and their fine aggregates can significantly improve the mechanical properties such as the compressive strength and flexural strength of the paving stone. In addition, the fine aggregate with a particle size of 0.075-0.3 mm can effectively fill the voids between the coarse aggregates, reduce the porosity inside the paving stone, improve the density, thereby reducing the accumulation of damage during freeze-thaw cycles and improving the durability.

[0051] Preferably, the magnesium oxide is light-burned magnesium oxide.

[0052] Compared with ordinary magnesium oxide, light-burned magnesium oxide has higher reaction activity and is more conducive to reacting with raw materials such as mineral powder and slag powder. Therefore, this technical solution preferably uses light-burned magnesium oxide as the magnesium oxide.

[0053] Furthermore, calculated by mass parts, the paving stone includes the following raw materials: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste residue particles, 26-30 parts of fine aggregate, and 7-8 parts of water; Calculated by mass parts, the waste residue inner core layer includes the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste residue, 0.1-0.5 parts of phosphate, and 7-10 parts of water.

[0054] This technical solution limits the raw material ratio of the paving stone and the raw material ratio of the waste residue inner core layer, which is beneficial to ensuring the performance of the paving stone.

[0055] Furthermore, the particle size of the arsenic-containing waste residue is <75 μm, and the specific surface area is >350 m 2 / g.

[0056] The smaller the particle size of the arsenic-containing waste residue, the larger the specific surface area, which is more conducive to increasing AsO in the arsenic-containing waste residue 4 3- being exposed and stabilized, thus facilitating the reduction of the arsenic leaching concentration; however, when the particle size is continuously reduced and the specific surface area is increased, the improvement effect is limited, and the production cost is likely to increase. Therefore, in this technical solution, the particle size of the arsenic-containing waste residue is limited to < 75 μm, and the specific surface area is limited to > 350 m 2 / g, which is conducive to reducing the arsenic leaching concentration at a relatively low cost and making the obtained paving stone meet the usage requirements.

[0057] Furthermore, calculated by mass percentage, the chemical components of the slag powder in the waste residue core layer and the barrier coating layer both include SiO 2 40 - 55%, Al 2 O 3 24 - 28%, Fe 2 O 3 5 - 7% and CaO 5 - 8%, and the rest is loss on ignition.

[0058] This technical solution preferably adds slag powder with a SiO 2 content of 45 - 60% and Al 2 O 3 content of 25 - 30% to the waste residue core layer and the barrier coating layer formulations, which is conducive to increasing the amount of gel generated in these two formulation systems of the waste residue core layer and the barrier coating layer, thereby facilitating the improvement of the strength of the paving stone and the reduction of the arsenic leaching content.

[0059] Preferably, calculated by mass percentage, the chemical components of the slag powder in the waste residue core layer and the barrier coating layer both include SiO 2 54%, Al 2 O 3 26.3%, Fe 2 O 3 6.5%, CaO 7.2% and MgO 0.9%, and the rest is loss on ignition.

[0060] Furthermore, calculated by mass percentage, the chemical components of the red mud include Al 2 O 3 15 - 20%, SiO 2 5 - 15%, Fe 2 O 3 30 - 40%, CaO 5 - 10% and Na 2 O 5 - 10%, and the rest is loss on ignition.

[0061] This technical solution preferably adds red mud with a CaO content of 5-10% calculated by mass percentage to the waste residue core layer formula system, which is beneficial to improving the alkaline environment in the waste residue core layer system and promoting the Al 2 O 3 and SiO 2 depolymerization. The products after depolymerization form hydrated magnesium silicate with a layered structure, magnesium aluminum hydrotalcite, and a hybrid gel network structure under alkaline conditions. Hydrated magnesium silicate, magnesium aluminum hydrotalcite, and the hybrid gel network structure can all fix AsO 4 3- , reducing the arsenic leaching concentration of the paving stone. In addition, the formation of the hybrid gel network structure is also beneficial to improving the strength of the paving stone.

[0062] Further illustration, the modulus of the sodium silicate is 1.2-1.4.

[0063] The modulus of sodium silicate refers to the molar ratio of SiO 2 to Na 2 O in its molecule. When the modulus of sodium silicate is 1.2-1.4, the free OH - produced by the hydrolysis of sodium silicate is relatively large, promoting the full depolymerization of Al 2 O 3 and SiO 2 in the mineral powder and slag powder, thus promoting the formation of calcium aluminosilicate gel and sodium aluminosilicate gel in the barrier coating layer, which is beneficial to ensuring the performance of the barrier coating layer.

[0064] Further illustration, calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH) 2 85-90%, SiO 2 3-3.5%, Fe 2 O 3 0.8-1%, Al 2 O 3 2-2.5% and MgO 0.8-1%, and the rest is the loss on ignition.

[0065] This technical solution preferably adds carbide slag with a Ca(OH) 2 content of 85-90% calculated by mass percentage to the paving stone formula, so that the OH - generated in the paving stone formula system is sufficient, thereby fully activating the activity of the mineral powder and generating calcium aluminosilicate gel to ensure the performance of the product.

[0066] Further explanation: The flexural strength of the paving stone is ≥5 MPa, the compressive strength is ≥48 MPa, the arsenic leaching concentration before soaking in the acetic acid buffer solution with a pH of 2.88 is ≤0.2 mg / L, and the arsenic leaching concentration after soaking in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3 mg / L.

[0067] Both the frost resistance test and the water erosion resistance test are important means to evaluate the durability of paving stones. The paving stones of this technical solution have met the qualified standards in both the frost resistance test and the water erosion resistance test, fully proving that the paving stones of this technical solution have good durability. At the same time, the arsenic leaching concentration of the paving stones of this technical solution before soaking in the acetic acid buffer solution with a pH of 2.88 is ≤0.2 mg / L, and the arsenic leaching concentration after soaking in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3 mg / L. The paving stones of this technical solution have excellent and persistent extremely low arsenic leaching toxicity. In addition, the flexural strength of this technical solution is ≥5 MPa, the compressive strength is ≥48 MPa, and it has high mechanical properties. Therefore, the paving stones prepared by this technical solution not only have excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stones on the premise of applying arsenic-containing waste residue to the paving stones and reducing production costs.

[0068] A preparation method of a paving stone added with arsenic-containing waste residue, which is used to prepare the paving stone added with arsenic-containing waste residue as described above, includes the following steps: A. Prepare core-shell waste residue particles; Mix the formula amounts of magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizing machine and dry it to obtain a waste residue inner core layer; Mix the formula amounts of slag powder, mineral powder, sodium silicate and water evenly to obtain a barrier coating slurry; Soak the waste residue inner core layer in the barrier coating slurry, take it out and after steam curing and room temperature curing, form a barrier coating layer on the surface of the waste residue inner core layer to obtain core-shell waste residue particles; B. Prepare paving stones: Mix the formula amounts of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material; Mix the core-shell waste residue particles, fine aggregate and the gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, vibrate and press it to obtain a plate; after sealing the plate and performing steam curing and room temperature curing, obtain the paving stone.

[0069] This technical solution also proposes a preparation method of a paving stone added with arsenic-containing waste residue, the steps of which are simple and highly operable, and are beneficial to avoiding the relevant properties of the paving stone during the preparation process.

[0070] Specifically, in the preparation of the paving stone slurry in this technical solution, part of the water is used to wet the core-shell waste residue particles and fine aggregates first, so that the core-shell waste residue particles and fine aggregates can be more easily wrapped and adhered by the cementitious material, thereby ensuring the strength of the paving stone.

[0071] Further explanation, in steps A and B, the curing temperature of the steam curing is 60-70°C, and the curing time is 48-74h; the curing time of the room temperature curing is 168-240h.

[0072] This technical solution limits the temperature and time of steam curing and the time of room temperature curing, improves the density of the product, reduces the fine pores, and improves the mechanical properties and durability of the product.

[0073] The technical solution of the present invention will be further described below through specific embodiments.

[0074] Test method: Flexural strength: The flexural performance is tested according to the test method of "GB / T 28635-2012 Concrete Pavement Bricks".

[0075] Compressive strength: The compressive strength is tested according to the test method of "GB / T 28635-2012 Concrete Pavement Bricks".

[0076] Frost resistance test: The frost resistance test is carried out according to the test method in Appendix E of "GB / T 28635-2012 Concrete Pavement Bricks". If there are basically no cracks on the surface of the paving stone after 50 freeze-thaw cycles, the mass loss rate < 5%, and the compressive strength loss < 25%, it is qualified.

[0077] ‌Water erosion resistance: The paving stone is soaked in water at 20±2°C for 48h, taken out and dried in an oven at 60±5°C for 48h, and the above soaking and drying steps are repeated 50 times. Then, visually inspect the cracks on the surface of the paving stone, and measure the mass, compressive strength and flexural strength of the paving stone. If there are basically no cracks on the surface of the paving stone, the mass loss rate < 5%, and the loss rates of the compressive strength and flexural strength are both < 25%, it is qualified.

[0078] Arsenic leaching concentration before soaking: The arsenic leaching concentration of the paving stone without being soaked in the acetic acid buffer solution with a pH of 2.88 is tested according to the test method of "GB18598-2019 Identification Standard for Toxicity of Hazardous Wastes - Leaching Toxicity Identification". If the arsenic leaching concentration ≤ 0.2mg / L, it is qualified. Among them, the preparation method of the acetic acid buffer solution with a pH of 2.88 is: add 5.7mL of glacial acetic acid to 500mL of deionized water. Add 64.3mL of 1mol / L NaOH solution, and make up to 1L with deionized water. Finally, adjust the pH to 2.88 (fine-tune with acetic acid or NaOH).

[0079] Arsenic leaching concentration after soaking: The arsenic leaching concentration of the paving stone soaked in acetic acid buffer solution with pH 2.88 for 30 days was tested according to the test method of "Identification Standard for Toxicity of Hazardous Wastes - Leaching Toxicity Identification" (GB18598-2019). If the arsenic leaching concentration ≤ 0.3 mg / L, it is qualified.

[0080] In the examples and comparative examples of the present invention, calculated by mass percentage, the mineral components of the arsenic-containing waste residue include 25% arsenopyrite, 30% pyrite, 40% quartz, and 5% secondary arsenate.

[0081] Calculated by mass percentage, the chemical composition of the slag powder in the waste residue inner core layer and the barrier wrapping layer both includes SiO 2 54%, Al 2 O 3 26.3%, Fe 2 O 3 6.5%, CaO 7.2%, and MgO 0.9%, and the rest is loss on ignition.

[0082] The mineral components of the red mud include goethite, and calculated by mass percentage, the chemical composition of the red mud includes Al 2 O 3 18%, SiO 2 13%, Fe 2 O 3 35%, CaO 8%, and Na 2 O 8%, and the rest is loss on ignition.

[0083] Calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH) 2 87%, SiO 2 3%, Fe 2 O 3 0.9%, Al 2 O 3 2%, and MgO 0.9%, and the rest is loss on ignition.

[0084] Example 1 In this example, calculated by mass parts, it includes the following raw materials: 5 parts of carbide slag, 3 parts of desulfurized gypsum, 20 parts of ore powder, 31 parts of core-shell waste residue particles, 26 parts of granite with a particle size of 0.075 mm, and 7 parts of water; The core-shell waste residue particles successively include a waste residue inner core layer and a barrier wrapping layer from the inside to the outside; Calculated by mass parts, the waste residue inner core layer includes the following raw materials: 8 parts of light-burned magnesia, 15 parts of ore powder, 15 parts of slag powder, 6 parts of red mud, 50 parts of arsenic-containing waste residue, 0.3 part of potassium phosphate, and 7 parts of water; the particle size of the arsenic-containing waste residue is 35 μm, and the specific surface area is 380 m 2 / g; Calculated by mass parts, the barrier coating layer comprises the following raw materials: 45 parts of slag powder, 38 parts of ore powder, 7 parts of sodium silicate with a modulus of 1.2, and 5 parts of water.

[0085] The preparation method of the paving stone added with arsenic-containing waste residue in this embodiment comprises the following steps: A. Prepare core-shell waste residue particles; Mix the formulated light-burned magnesia, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate, and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and after drying, obtain a waste residue inner core layer with a particle size of 5 mm; Mix the formulated slag powder, ore powder, sodium silicate, and water evenly to obtain a barrier coating slurry; Immerse the waste residue inner core layer in the barrier coating slurry, take it out, cure it in steam at 60 °C for 50 h and cure it at room temperature for 168 h, and then form a barrier coating layer with a thickness of 2 mm on the surface of the waste residue inner core layer to obtain core-shell waste residue particles with a particle size of 7 mm; B. Prepare paving stones: Mix the formulated carbide slag, desulfurized gypsum, ore powder, and water evenly to obtain a gel material; Mix the core-shell waste residue particles, fine aggregate, and gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, vibrate and press for 0.5 min to obtain a plate; after sealing the plate and curing it in steam at 60 °C for 50 h and curing it at room temperature for 168 h, obtain paving stones.

[0086] Example 2 In this embodiment, calculated by mass parts, it comprises the following raw materials: 5 parts of carbide slag, 3.5 parts of desulfurized gypsum, 22 parts of ore powder, 34 parts of core-shell waste residue particles, 28 parts of limestone with a particle size of 0.1 mm, and 7 parts of water; The core-shell waste residue particles successively comprise a waste residue inner core layer and a barrier coating layer from the inside to the outside; Calculated by mass parts, the waste residue inner core layer comprises the following raw materials: 10 parts of light-burned magnesia, 20 parts of ore powder, 18 parts of slag powder, 6 parts of red mud, 50 parts of arsenic-containing waste residue, 0.2 parts of sodium phosphate, and 8 parts of water; the particle size of the arsenic-containing waste residue is 25 μm, and the specific surface area is 400 m 2 / g; Calculated by mass parts, the barrier coating layer comprises the following raw materials: 50 parts of slag powder, 38 parts of ore powder, 8 parts of sodium silicate with a modulus of 1.3, and 5 parts of water.

[0087] The preparation method of the paving stone added with arsenic-containing waste residue in this embodiment comprises the following steps: A. Prepare core-shell waste residue particles; Mix the formula amount of light-burned magnesium oxide, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and after drying, obtain a waste residue inner core layer with a particle size of 8 mm; Mix the formula amount of slag powder, ore powder, sodium silicate and water evenly to obtain a barrier coating slurry; Soak the waste residue inner core layer in the barrier coating slurry, take it out and cure it in 65°C steam for 48 h and cure it at room temperature for 240 h, then a barrier coating layer with a thickness of 3 mm is formed on the surface of the waste residue inner core layer, and core-shell waste residue particles with a particle size of 11 mm are obtained; B. Prepare paving stones: Mix the formula amount of carbide slag, desulfurized gypsum, ore powder and water evenly to obtain a gel material; Mix the core-shell waste residue particles, fine aggregate and gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, vibrate and press for 0.6 min to obtain a plate; after sealing the plate and curing it in 65°C steam for 48 h and curing it at room temperature for 240 h, paving stones are obtained.

[0088] Example 3 In this example, calculated by mass fraction, it includes the following raw materials: 6 parts of carbide slag, 2.5 parts of desulfurized gypsum, 20 parts of ore powder, 32 parts of core-shell waste residue particles, 30 parts of feldspar with a particle size of 0.3 mm and 7.5 parts of water; The core-shell waste residue particles sequentially include a waste residue inner core layer and a barrier coating layer from the inside to the outside; Calculated by mass fraction, the waste residue inner core layer includes the following raw materials: 10 parts of light-burned magnesium oxide, 17 parts of ore powder, 15 parts of slag powder, 6 parts of red mud, 45 parts of arsenic-containing waste residue, 0.1 part of ammonium phosphate and 7 parts of water; the particle size of the arsenic-containing waste residue is 40 μm, and the specific surface area is 370 m 2 / g; Calculated by mass fraction, the barrier coating layer includes the following raw materials: 45 parts of slag powder, 37 parts of ore powder, 7 parts of sodium silicate with a modulus of 1.2 and 6 parts of water.

[0089] The preparation method of the paving stone adding arsenic-containing waste residue in this example includes the following steps: A. Prepare core-shell waste residue particles; Mix the formula amount of light-burned magnesium oxide, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and after drying, obtain a waste residue inner core layer with a particle size of 10 mm; Mix the formula amount of slag powder, ore powder, sodium silicate and water evenly to obtain a barrier coating slurry; Soak the waste residue core layer in the barrier coating slurry, take it out, and after steam curing at 70 °C for 48 h and curing at room temperature for 200 h, a barrier coating layer with a thickness of 2 mm is formed on the surface of the waste residue core layer, and core-shell waste residue particles with a particle size of 12 mm are obtained; B. Preparation of paving stones: Mix the formula amounts of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material; Mix the core-shell waste residue particles, fine aggregate and gel material evenly to obtain paving stone slurry; pour the paving stone slurry into a mold, and after vibrating and pressing for 0.8 min, obtain a plate; after sealing the plate and steam curing at 70 °C for 48 h and curing at room temperature for 200 h, paving stones are obtained.

[0090] Comparative Example 1 Use the existing preparation method to prepare paving stones, that is, mix 10 parts of lime, 20 parts of polyferric sulfate, 15 parts of dolomite sand, 15 parts of cement and 30 parts of water evenly to obtain a composite curing agent, and mix 30 parts of the composite curing agent with 40 parts of arsenic-containing waste residue evenly to obtain paving stone slurry. Pour the paving stone slurry into a mold, and after vibrating and pressing for 0.5 min, obtain a plate; after sealing the plate and steam curing at 60 °C for 48 h and curing at room temperature for 168 h, paving stones are obtained.

[0091] Comparative Example 2 The preparation method and raw materials of Comparative Example 2 are the same as those of Example 2, except that light-burned magnesia is not added to the waste residue core layer formula in Comparative Example 2.

[0092] Comparative Example 3 The preparation method and raw materials of Comparative Example 3 are the same as those of Example 2, except that a barrier coating layer is not formed on the surface of the waste residue core layer in Comparative Example 3, that is, the core-shell waste residue particles in Comparative Example 3 only include the waste residue core layer.

[0093] Comparative Example 4 The preparation method and raw materials of Comparative Example 4 are the same as those of Example 2, except that sodium silicate is not added to the barrier coating layer formula in Comparative Example 4.

[0094] Comparative Example 5 The preparation method and raw materials of Comparative Example 5 are the same as those of Example 2, except that core-shell waste residue particles are not added to the paving stone formula in Comparative Example 5.

[0095] Conduct performance tests on the paving stones prepared in the above examples and comparative examples, and the specific test results are shown in Table 1.

[0096] Table 1 Relevant performance test results of paving stones

[0097] Both the frost resistance test and the water erosion resistance test are important means to evaluate the durability of paving stones. It can be seen from the test data in Table 1 that the paving stones prepared by this technical solution meet the qualified standards in both the frost resistance test and the water erosion resistance test, fully demonstrating that the paving stones of this technical solution have good durability. At the same time, the arsenic leaching concentration of the paving stones of this technical solution before being soaked in the acetic acid buffer solution with a pH of 2.88 is ≤0.2 mg / L, and the arsenic leaching concentration after being soaked in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3 mg / L. The paving stones of this technical solution have excellent and persistent extremely low arsenic leaching toxicity. In addition, the flexural strength of this technical solution is ≥5 MPa, and the compressive strength is ≥48 MPa, with relatively high mechanical properties. Furthermore, through comparative experiments, it is found that the paving stones obtained by using this technical solution (i.e., a preparation method of paving stones adding arsenic-containing waste residue) are superior to the paving stones in Comparative Example 1 (i.e., the prior art) in terms of various performance test indicators. Therefore, the paving stones obtained by the preparation method of paving stones adding arsenic-containing waste residue of this technical solution not only have excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of paving stones on the premise of applying arsenic-containing waste residue to paving stones and reducing production costs.

[0098] In Comparative Example 2, since light-burned magnesium oxide was not added to the waste residue inner core layer formula, magnesium oxide could not hydrolyze to generate magnesium ions that could individually fix arsenate. In addition, due to the lack of magnesium ions in the waste residue inner core layer formula system, it also led to the inability to generate magnesium silicate hydrate and arsenic acid intercalated aluminum magnesium hydrotalcite that could fix arsenate in the waste residue inner core layer formula, resulting in a poor fixing effect on arsenate and thus an increase in arsenic leaching concentration.

[0099] In Comparative Example 3, due to the absence of a barrier coating layer, the following defects occurred in many aspects: (1) The barrier coating layer could have enhanced the core-shell waste residue particles and improved the mechanical properties such as flexural and compressive strength of the paving stones. However, due to the lack of this structure, the mechanical properties of the paving stones decreased. (2) The barrier coating layer has the ability to fix arsenate. Without this barrier coating layer, the arsenate in the waste residue inner core layer is likely to react with the sulfate ions in ettringite to form arsenic-type ettringite, which not only further reduces the mechanical properties of the paving stones but also leads to a decrease in their durability. (3) The lack of the fixing effect of the barrier coating layer on arsenate reduces the stability of arsenate in the paving stones and increases the arsenic leaching concentration. In addition, the barrier coating layer has acid and alkali resistance characteristics and can inhibit the leaching of arsenate in acidic or alkaline environments. Without setting this coating layer, the arsenic leaching concentration of the paving stones in acidic or alkaline environments increases significantly.

[0100] In Comparative Example 4, since sodium silicate is not added to the barrier coating formula, it is impossible to alkaline-excite the mineral powder and slag powder in the barrier coating to form a mixed gel network composed of calcium aluminum silicate gel and sodium aluminum silicate gel, which results in the barrier coating failing to achieve the barrier coating's reinforcing effect on the core-shell waste slag particles, causing the mechanical properties of the paving stones, such as flexural strength and compressive strength, to deteriorate. At the same time, the barrier coating's fixation of arsenate also depends on its internal gel network structure. Since the gel network cannot be formed, the barrier coating cannot effectively fix the arsenate, making it easy for the arsenate in the inner core layer of the waste slag to undergo a substitution reaction with the sulfate ions in the calcium sulfonate to form arsenic-type calcium sulfonate, which not only further weakens the mechanical properties of the paving stones, but also affects their durability. In addition, since the barrier coating cannot effectively fix the arsenate, the arsenic element in the paving stones is more easily leached, resulting in an increase in the arsenic leaching concentration. At the same time, the barrier coating layer that has not formed an effective gel network has also lost its original acid and alkali resistance, causing the arsenic leaching concentration of the paving stones in an acidic or alkaline environment to increase significantly.

[0101] In Comparative Example 5, since the core-shell waste particles were not added to the paving stone formula, the strength and durability of the paving stones deteriorated.

[0102] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the scope of protection of the present invention.

Claims

1. A paving stone with arsenic-containing waste residue added, characterized in that: The raw materials include carbide slag, desulfurized gypsum, mineral powder, core-shell waste slag particles, fine aggregate and water; wherein the particle size of the core-shell waste slag particles is 7 to 13 mm; and the content of calcium hydroxide in the carbide slag is ≥8% calculated by mass percentage; The core-shell waste slag particles include a waste slag core layer and a barrier wrapping layer from the inside to the outside; The waste slag inner core layer comprises the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste slag, phosphate and water; wherein the mineral components of the arsenic-containing waste slag include arsenopyrite; the mineral components of the red mud include goethite, and the chemical components of the red mud include CaO; Calculated by weight, the barrier wrapping layer includes the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water; The chemical compositions of the slag powder in the waste slag inner core layer and the barrier wrap layer include SiO2, Al2O3 and CaO.

2. The paving stone with arsenic-containing waste residue added according to claim 1, characterized in that: Calculated by weight, the floor paving stone includes the following raw materials: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste slag particles, 26-30 parts of fine aggregate and 7-8 parts of water; Calculated by mass, the inner core layer of the waste slag includes the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste slag, 0.1-0.5 parts of phosphate and 7-10 parts of water.

3. The paving stone added with arsenic-containing waste slag according to claim 1, characterized in that: The particle size of the arsenic-containing waste residue is less than 75 μm, and the specific surface area is greater than 350 m 2 / g.

4. The paving stone with arsenic-containing waste residue added according to claim 1, characterized in that: Calculated by mass percentage, the chemical compositions of the slag powder in the waste slag inner core layer and the barrier wrap layer include SiO2 40-55%, Al2O3 24-28%, Fe2O3 5-7% and CaO 5-8%, with the remainder being loss on ignition.

5. The paving stone added with arsenic-containing waste residue according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition of the red mud includes Al2O3 15-20%, SiO2 5-15%, Fe2O3 30-40%, CaO 5-10% and Na2O 5-10%, and the rest is loss on ignition.

6. The paving stone added with arsenic-containing waste slag according to claim 1, characterized in that: The modulus of the sodium silicate is 1.2 to 1.

4.

7. The paving stone added with arsenic-containing waste residue according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH)2 85-90%, SiO2 3-3.5%, Fe2O3 0.8-1%, Al2O3 2-2.5% and MgO 0.8-1%, and the rest is ignition loss.

8. The paving stone added with arsenic-containing waste slag according to claim 1, characterized in that: The flexural strength of the paving stone is ≥5MPa, the compressive strength is ≥48MPa, the arsenic leaching concentration before being soaked in an acetic acid buffer solution with a pH of 2.88 is ≤0.2mg / L, and the arsenic leaching concentration after being soaked in an acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3mg / L.

9. A method for preparing paving stones with arsenic-containing waste residue, characterized in that: The method for preparing the paving stone added with arsenic-containing waste residue as claimed in any one of claims 2 to 8 comprises the following steps: A. preparing core-shell waste slag particles; The magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water are mixed evenly to obtain a waste residue modified mixture; the waste residue modified mixture is fed into a pelletizing machine, and after drying, a waste residue inner core layer is obtained; The slag powder, mineral powder, sodium silicate and water in the formula are evenly mixed to obtain a barrier coating slurry; The waste slag inner core layer is immersed in a barrier coating slurry, taken out and subjected to steam curing and room temperature curing, so that a barrier coating layer is formed on the surface of the waste slag inner core layer to obtain core-shell waste slag particles; B. Preparation of paving stones: Evenly mixing the formulated amounts of carbide slag, desulfurized gypsum, mineral powder and water to obtain a gel material; The core-shell waste particles, fine aggregates and gel materials are uniformly mixed to obtain floor paving stone slurry; the floor paving stone slurry is poured into a mold and vibrated to obtain a board; the board is sealed and subjected to steam curing and room temperature curing to obtain the floor paving stone.

10. The method for preparing paving stones with arsenic-containing waste residue added according to claim 9, characterized in that: In step A and step B, the curing temperature of the steam curing is 60-70° C., and the curing time is 48-74 hours; the curing time of the room temperature curing is 168-240 hours.

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